Ultraviolet light has been successfully utilized in the treatment of allergic and autoimmune skin diseases for decades as it prevents the development of antigen induced cellular immune response and induces immune tolerance. (Streilein J W, Bergstresser P R: Genetic basis of ultraviolet-B on contact hypersensitivity. Immunogenetics 27: 252-258, 1988). The immunosuppressive effect of ultraviolet radiation can mainly be associated with the inhibition of antigen presentation and the induction of apoptosis in T cells. Both ultraviolet B light-therapy (280-320 nm) and ultraviolet A irradiation (320-400 nm) following a pre-treatment with the photosensitizing agent psoralen can successfully inhibit the immunological processes in the skin.
Several light-therapy devices are available for treatment of certain dermatological disorders (e.g. psoriasis, atopic dermatitis) by therapeutic ultraviolet irradiation of the skin. Previously, for purposes of ultraviolet light therapy, devices emitting broad-band ultraviolet B (BB-UVB) radiation were used. Recently, the more effective narrow-band ultraviolet B (NB-UVB) systems have become common as they minimize the delivery of ultraviolet B radiation of less than 300 nm wavelength, which is responsible for inflammation but mainly lacks therapeutic effect. (Degitz K, Messer G, Plewig G, Röcken M: Schmalspektrum-UVB 311 nm versus Breitspektrum-UVB. Neue Entwicklungen in der Phototherapie. Hautarzt 49: 795-806, 1998). Our studies performed in psoriatic patients have demonstrated that xenon chloride excimer laser emitting ultraviolet B light of 308 nm wavelength provides an even greater therapeutic effect. (Bónis B, Kemény L, Dobozy A, Bor Zs, Szabó G, Ignácz F: 308 nm UVB excimer laser for psoriasis. The Lancet 35: 1522, 1997; Kemény L, Bónis B, Dobozy A, Bor Z, Szabo G, Ignacz F: 308-nm excimer laser therapy for psoriasis. Arch Dermatol. 137: 95-96, 2001; Novak Z, Bónis B, Baltás E, Ocsovszki I, Ignácz F, Dobozy A, Kemény L: The xenon chloride ultraviolet B laser is more effective in treating psoriasis and in inducing T cell apoptosis than narrow-band ultraviolet B. J Photochem Photobiol B 67:32-38, 2002).
Apart from the type of the light therapy system, the effectiveness of the treatment is further influenced by the reflection of the ultraviolet radiation from the skin surface. On a dry and scaly desquamating skin surface, the reflection of ultraviolet light is increased. As a result, only a lower proportion of the radiation will penetrate the skin and the therapeutic effect will be decreased. The problem is under active investigation and a number of different mechanical devices and methods have been and are still being developed to modify the optical properties of biological tissues (Rylander Cristopher G. et al.: US20070159592 patent application).
However, there are not only mechanical but also chemical solutions available to address the problem. Paraffin oil is often administered to the skin surface prior to ultraviolet irradiation to prevent its reflection and therefore enhance the effectiveness of light therapy. Paraffin oil itself does not absorb ultraviolet radiation but reduces skin desquamation which are together responsible for its beneficial effect. In the clinical setting, however, pre-treatment with paraffin oil is only rarely performed due to the cosmetically not acceptable nature of the substance, which stains clothing and causes patients to have difficulties with getting dressed after the treatment. On the other hand, other compositions, which are cosmetically favourable, often absorb ultraviolet light and therefore decrease the effectiveness of light therapy. Application of higher doses of ultraviolet B radiation, however, may lead to adverse effects.
Optical enhancement of skin transmittance may result in greater effectiveness of light therapy, but it has been proven that for therapeutic purposes, the most effective part of ultraviolet B spectrum is the range between 310 and 320 nm wavelength. Ultraviolet B radiation ranging from 280 to 320 nm wavelength has only a lower therapeutic effect while causing more severe skin inflammation. Therefore, an effective method is required to facilitate the penetration of ultraviolet B radiation of appropriate wavelength into the skin by reducing reflection from the skin surface, as well as to prevent the penetration of shorter wavelength components of ultraviolet B spectrum, therefore, reducing skin inflammation.